Poly(styrene-b-isobutylene-b-styrene) (SIBS) is a thermoplastic elastomer that has gained attention recently due to its high degree of biocompatibility. Due to its biocompatibility, SIBS has been found to be useful for a variety of applications, such as stent coating, glaucoma shunt, and tubing. This linear block copolymer has a triblock structure formed by a polyisobutylene (PIB) core sandwiched between blocks of polystyrene (PS). The formulation of SIBS can be tailored for different applications by changing the weight percentage of PS or by changing the molecular weight of the polymer chains. The hard PS blocks provide SIBS with a glassy microstructure that enhances mechanical strength and rigidity of the material, while the PIB has a soft microstructure with increased chain mobility that gives the polymer its elastomeric properties. The possibility of tailoring mechanical properties, together with the high degree of biocompatibility, makes SIBS an ideal material for use in biomedical devices.
However, there is a high cost associated with making SIBS. The high cost (30-40%) of most SIBS products is largely due to the expensive bifunctional polymerization initiator needed for synthesis. Typically, that expensive bifunctional polymerization initiator is 1-(tert-butyl)-3,5-bis(2-chloropropan-2-yl)benzene (abbreviated herein as HDCCl, for hindered dicumyl chloride):
